Silver halide light sensitive photographic materials, which have superior properties such as high sensitivity and excellent tone reproduction as compared to other print materials, are broadly employed. An image forming method has been known, employing amplification development of a silver halide photographic material, in which advantageous effects of the silver halide photographic material are displayed, the consumed amount of silver halide can be reduced, and which is preferable in terms of effective usage of natural resource. As examples of the amplification development is cited a method in which an oxidized color developing agent is formed by using an oxidizing agent such as hydrogen peroxide or a cobalt (III) complex in the presence of developed silver as a catalyst and subsequently, a dye image is formed upon reaction with a coupler.
In conventional color development, an oxidized developing agent which takes part in dye image-forming, results from redox reaction between the developing agent and silver halide having a latent image, so that the amount of silver halide to be used in the photographic material is optimally adjusted in proportion to that of the coupler. After reached a sufficient density, there is shown behavior such that the characteristic curve changes slightly, for a while, in a manner of parallel displacement. Thus, as a result of a region in which an increase of the minimum density is substantially restrained (a so-called saturated stable region) being present, there can be consistently obtained characteristics of only a little increase of the minimum density, which is important in print material, even when development is prolonged. In amplification development, contrarily, an oxidized developing agent which takes part in dye image-forming, is produced from a redox reaction between the developing agent and an oxidizing agent, in which the developing agent and the oxidizing agent are generally present in excess, as compared to the coupler to achieve sufficient reaction. As a result, even after the amplification development proceeds and reaches a sufficient density, contrast at a higher density portion still varies and an appreciable increase of the minimum density occurs. Thus, there is little or no region such as a saturated stable region, as in conventional development, so that even slightly prolonged development tends to result in a marked increase of the minimum density. Obviously, improvements thereof are desired.
A photographic material having on a support plural layers capable of forming different color image is conventionally employed to obtain color images. When such photographic material is subjected to amplification development, there tends to occur a so-called interlayer effect in which variation of the dye forming amount in the upper layer affects kinetics of development in the lower layer, making it difficult to stably reproduce contrast. In conventional color development, even if development in the upper layer affects developability of the lower layer, developing time can be adjusted so as to obtain optimum development of the lower layer within the time the upper layer is in the saturated stable region, leading to characteristics of little increase of the minimum density and variation of contrast or contrast balance, which are important for print materials. In the amplification development, however, the above-described saturated stable region is not present, so that, when the dye forming amount of the upper layer changes with exposure, its effect on the lower layer can not be compensated for by adjusting the developing time, making difficult stable tone reproduction. This phenomenon is marked in the case when the dye forming amount varies in a dye image forming layer farthest from )or uppermost on) a support, and improvements thereof are sought.
Variation in developability of the lower layer due to the variation of the dye forming amount of the upper layer becomes inappreciable, when the time for amplification development is shortened. However, shortening of the amplification development results in insufficient maximum density. Accordingly, there is incompatibility between a higher maximum density and lower minimum density, and stable tone reproduction of the lower layer in response to variation of the dye forming amount of the upper layer.